Photoelectrochemical Determination of the Absolute Band Edge Positions as a Function of Particle Size for ZnO Quantum Dots
Photoelectrochemical Determination of the Absolute Band Edge Positions as a Function of Particle Size for ZnO Quantum Dots
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DOI：
10.1021/jp302220w
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发表时间：
2012-07-26
影响因子：
3.7
通讯作者：
Edvinsson, Tomas
中科院分区：
文献类型：
--
作者：
Jacobsson, T. Jesper;Edvinsson, Tomas
用电势相关吸收光谱法测定了ZnO量子点导带和价带边的绝对位置随量子点粒径的变化。能带边缘的绝对位置对于在表面发生的催化反应至关重要。它们也是纳米颗粒太阳能电池和其他基于纳米颗粒的光电器件中电荷注入和提取的关键参数。导带边缘的位置通过导带态的恒电位布居并监测光学带隙的增加来确定。这是在量子限制区域中的ZnO颗粒进行的，其直径范围在4和9 nm之间。将颗粒沉积成薄膜，得到可以进行分析的颗粒集合。推导了相关方程，并对其有效性进行了定量分析。我们发现，基本上所有的量子尺寸效应的带隙增加发生的导带边的移位。抛物近似，这是在分析中的假设之一，的有效性的程度进行了研究，无论是实验和密度泛函理论计算的散装ZnO在这里，我们发现，抛物近似仅在略小于0.1 eV的导带边缘的能量范围内是有效的，但在该制度构成了一个很好的近似。我们还证明了抛物线近似的有效性如下的费米能级上升到导带能级。
The absolute position of the conduction and the valence band edges of ZnO quantum dots (Qdots) has been determined as a function of particle size with potential dependent absorption spectroscopy. The absolute position of the band edges are vital for which catalytic reactions that can occur at the surface. They are also crucial parameters for charge injection and extraction in nanoparticular solar cells and other optoelectronic devices based on nanoparticles. The position of the conduction band edge was determined by potentiostatic population of the conduction band states and monitoring the resulting increase in the optical band gap. This was performed for ZnO particles in the quantum confined region with diameters ranging between 4 and 9 nm. The particles were deposited into thin films giving an ensemble of particles for which the analysis could be performed. The relevant equations were derived and their validity in terms of applied potential and kinetic considerations was quantified. We find that essentially all of the quantum size effect of increased band gap is occurring by a shift of the conduction band edge. The extent of the validity of the parabolic approximation, which is one of the assumptions in the analysis, is investigated, both experimentally and with density functional theory calculations of bulk ZnO Here, we find that the parabolic approximation only is valid in an energy range of slightly less than 0.1 eV from the conduction band edge but in that regime constitutes an excellent approximation. We also demonstrate that the validity of the parabolic approximation follows a rising Fermi level into the conduction band energy levels.